Aspects of the present disclosure relate generally to wireless communications and, more particularly, to a method and an apparatus for searching for service when a multi-mode user equipment (UE) goes out of service (OOS).
Wireless communication networks are widely deployed to provide various communication services such as telephony, video, data, messaging, broadcasts, and so on. Such networks, which are usually multiple access networks, support communications for multiple users by sharing the available network resources. One example of such a network is the UMTS Terrestrial Radio Access Network (UTRAN). The UTRAN is the radio access network (RAN) defined as a part of the Universal Mobile Telecommunications System (UMTS), a third generation (3G) mobile phone technology supported by the 3rd Generation Partnership Project (3GPP). The UMTS, which is the successor to Global System for Mobile Communications (GSM) technologies, currently supports various air interface standards, such as Wideband-Code Division Multiple Access (W-CDMA), Time Division-Code Division Multiple Access (TD-CDMA), and Time Division-Synchronous Code Division Multiple Access (TD-SCDMA). The UMTS also supports enhanced 3G data communications protocols, such as High Speed Packet Access (HSPA), which provides higher data transfer speeds and capacity to associated UMTS networks.
A public land mobile network (PLMN) is a network that is operated by an administrator or a recognized operating agency (ROA) (which may both be referred to as an “operator”) for the specific purpose of providing land and/or mobile telecommunication services to the public. A PLMN is identified by PLMN identifier (PLMN ID) which includes a Mobile Country Code (MCC) and a Mobile Network Code (MNC). Each operator providing mobile services has its own PLMN identifier. PLMNs interconnect with other PLMNs and Public switched telephone networks (PSTN) for telephone communications and/or with Internet service providers for data and Internet. Access to PLMN services may be achieved via an air interface involving radio communications between mobile phones and/or other wireless-enabled user equipment (UE) and land-based radio transmitters, radio base stations, and/or fiber optic networks.
A subscriber to wireless services may be associated with a subscriber profile. The subscriber's profile may be stored in association with a home public land mobile network (HPLMN), which simply may be a PLMN associated with a wireless service to which the subscriber has a relationship and/or subscription. If the subscriber roams to another PLMN by, for example, leaving a geographic area associated with the subscriber's HPLMN, the subscriber may still receive subscription information from its HPLMN even though the subscriber may now be receiving service from a visited public land mobile network (VPLMN). A HPLMN for one subscriber may be a VPLMN for another subscriber.
When a multi-mode UE, e.g., a UE that is capable of operating across different standards and radio access technologies (RAT), goes out-of-service (OOS), the Non-Access Stratum (NAS) layer of the UE sends a service request to a radio resource on the UE to search for service on a PLMN from which the UE was most recently receiving service. The most recent PLMN may be referred to as the registered PLMN or RPLMN. The RPLMN may be the HPLMN or a VPLMN. When the UE is operating in UMTS or LTE, the radio resource may be referred to as a radio resource control (RRC) and when the UE is operating in GSM, the radio resource may be referred to as RR.
The UE may search for service on a RAT-by-RAT basis. First, the UE may perform a scan of a first RAT associated with the RPLMN. If a signal on which service may be acquired is found, the UE may attempt to camp on the signal and register with the RPLMN. If not, the UE may scan in the current RAT (associated with the RPLMN) according to an acquisition database (ACQ DB). The ACQ DB includes information related to frequencies on which the UE is most likely to find a signal where service may be acquired within each PLMN that is accessible by the UE for each RAT supported by each PLMN. More particularly, the ACQ DB may include a list of frequencies that are each associated with a PLMN identifier and a RAT identifier.
If the UE finds an acceptable signal on the first RAT associated with the RPLMN as a result of the scanning frequencies identified within the ACQ DB, which may be referred to as an ACQ DB scan, the UE may attempt to register with the RPLMN. If no such signal is found, the UE may perform a full band scan for the first RAT associated with the RPLMN. If the UE finds an acceptable signal while scanning the full band, the UE may attempt to register with the RPLMN. If the UE has not been able to register with the RPLMN upon completion of the ACQ DB and full band scans of each RAT associated with the RPLMN, the UE may provide a list of all available PLMNs to the Non-Access Stratum (NAS).
It is often the case that a UE may find service in a RAT associated with a PLMN at the frequencies corresponding to the RAT and the PLMN within the ACQ DB. In other words, the ACQ DB may include PLMN-RAT-frequency combination information that indicates the most promising candidates for camping and registration. However, the current techniques perform an ACQ DB scan and then a full band scan for a first RAT before performing ACQ DB scans and then a full band scan for the next RAT. As such, the UE may spend a large amount of time performing a large number of scans in order to acquire service. As a result, there may be an undesirable delay in the UE acquiring service.
As such, an optimized search for service when a multi-mode UE goes out of service (OOS) is desired.